Interpretive Summary: Rare and unusual insect phenotypes can provide very useful data to entomologists. Bilateral gynandromorphs are phenotypes that are half-male and half-female. Such unusual specimens have helped taxonomists indentify male characters essential for keying bee species when only females are frequently encountered. The behavioral repertoires of gynanders that survive into adulthood can also provide new insights into the origins of insect reproductive behavior. Our living gynander specimen indicates that insect behavior and morphology have different centers of control, which can vary considerably among genetic mosaics.

Technical Abstract:
We report for the first time on the courtship behavior of a gynandromorph of a solitary bee. Such observational studies on a living specimen that is bilaterally male and female can indentify centers of control for specific insect behaviors. Our observations show that gender in bees is not linked to morphology and is likely affected by a completely different set of neural centers. Our gynander was clearly female-dominant with high sex appeal, despite being unable to mate successfully. We suspect that our bee gynander in Osmia ribifloris, as in other species, can occur when eggs are genetically damaged by extreme temperature changes. We expect greater environmental variation for pollinator species intended for active management, and therefore the incidences of such rare phenotypes might increase.